A conducted energy weapon (CEW), variously known as an electronic disabling device, an electronic control device, or a “stun gun”, incapacitates a targeted subject by delivering a sequence of high voltage pulses to the skin by means of a pair of electrodes. Current which flows between the electrodes stimulates the target's neuromuscular system to produce involuntary muscle contractions, thereby disabling the subject. Depending on CEW design, the electrodes may contact the skin through direct application of the weapon to the subject's body, or by means of darts launched from the weapon which then penetrate the clothing of the target to reach the skin.
In law enforcement, a CEW may be used by a peace officer for subduing a combative person in a scenario where application of significant but non-lethal restraining force is necessary to secure safety of the peace officer and potentially the public. Although a CEW is intended to be non-lethal, deaths have occurred in a limited number of cases where such weapons have been used. Although specific cause of death may be difficult to identify, an underlying medical or drug-induced condition in combination with a delirious mental state can be contributors to an outcome known to forensic science as “sudden death following restraint” (SDFR). To what extent CEW use may have contributed to fatality in SDFR cases is controversial, and such controversy raises concern in the general public regarding safety of the weapons and the perceived risks of their use.
A scenario which has received less public attention but is of significant concern to law enforcement agencies is a situation in which a CEW is discharged but fails to incapacitate the intended target. Such failure will arise in the case of a missed target, resulting in poor or no electrical contact from one or both projectile darts to the skin of the intended victim. In cases where evidence of effective electrode contact can be verified, a negative outcome may then be attributable to reduced performance or malfunction of the weapon.
Public concerns over safety and perceived risks of CEWs have prompted law enforcement agencies to internally conduct or to commission laboratory-based studies of CEWs. To assist such agencies with their investigations, a leading manufacturer of CEWs has provided a document illustrating the recommended test methods. In summary, the manufacturer's tests include use of an oscilloscope and accessory probes to observe output current delivered by the weapon to a specified resistive load, and to observe peak sparking voltage developed across a high-impedance probe. Such methods are limited in that they require significant technical expertise in setup and use of the apparatus. More importantly, since CEW operation fundamentally relies on generation of spark discharges across one or more air gaps internal to the weapon, CEW signals as displayed by an oscilloscope may be corrupted by impulse artifacts, thus requiring significant skill on the part of the user of the apparatus to discern the true characteristics of the CEW signal from the superimposed impulse noise.
Performed in accordance with such testing instructions provided by the CEW manufacturer, one study conducted at the Canadian Police Research Center (CPRC) produced discrepant results which were later uncovered and questioned in a television news report produced by the Canadian Broadcasting Corporation (CBC). Additionally, the CBC report went further to describe a subsequent independent laboratory investigation performed at National Technical Systems (NTS), which found three CEWs out of a sample of 44 which failed to produce any output, and four weapons which produced output which was 47-58% higher than specified by the manufacturer. CEW tests performed by another commercial laboratory found 96 out of 122 TASER® M26 weapons tested failed to meet one or more of the manufacturer's performance specifications, causing the government which commissioned the laboratory tests to remove the weapons from police service. These negative results demonstrate a need exists to periodically test CEWs to guarantee that weapons in use are, at minimum, operating within manufacturer-specified limits.
Following an incident at the Vancouver International Airport in October 2007, in which Robert Dziekanski died after receiving several shocks from a CEW discharged by an officer of the Royal Canadian Mounted Police (RCMP), a strong and international public reaction ensued when an amateur video of the incident became widely seen on television and the Internet. In February 2008, the government of British Columbia commissioned retired justice Thomas Braidwood Q.C. to inquire into and report on the use of CEWs by law enforcement agencies operating within the province. After receiving presentations on CEWs from numerous experts with medical, engineering, law enforcement and commercial backgrounds, the Braidwood Commission issued a report to the BC provincial government in June 2009 specifying nineteen recommendations on CEW usage, including requirements for periodic testing of electrical output from all CEWs in use, and in particular, testing of any CEW involved in an incident where there is significant injury or death.
In response to public pressure, law enforcement agencies such as the RCMP have acknowledged the Braidwood recommendations and have initiated processes to adopt them. Compliance places significant economic and logistic burdens on such agencies, who must either internally develop the required technical resources and engineering competence to perform the recommended tests, or alternatively solicit costly testing services from external laboratories.
A limitation of CEW tests performed by government research and commercial laboratories is that specialist knowledge and experience is required to set up the necessary experiments and to correctly interpret signals which may be corrupted by impulse interference as previously described. High Voltage Test Techniques by Dieter Kind and Kurt Feser (ISBN 0750651830) is a reference text which will be familiar to persons skilled in the arts of electrical engineering or physics, and in particular, to those having an interest in experimental measurement of hazardous voltages and electrical currents such as would be encountered in testing a CEW. Apparatus and methods as taught by Kind and Feser are not suitable for use by peace officers or other personnel who may be associated with a law enforcement agency, and who may have limited understanding of high-voltage engineering and little or no training in the use of related laboratory apparatus and techniques.
A further limitation of CEW tests performed by government research and commercial laboratories is that the tests are entirely focussed on CEW conformance to the manufacturer's performance specifications. In such tests, a CEW is considered acceptable for use if all tested parameters fall within corresponding limits specified by the weapon manufacturer. However, as reported in the scientific literature and summarized in the first report published by the Braidwood Commission, there exists a growing body of scientific evidence to indicate that there may be a non-zero risk of fatal cardiac arrhythmia that may result from stimulation produced by a “normal” CEW. On the other hand, a CEW which marginally exceeds minimum specified performance levels in several tested parameters may be acceptable for use by definition, however, risk of failure to subdue a combative individual may be greater compared to a CEW having all tested parameters well within their respective acceptance ranges. These considerations motivate a superior metric for CEW acceptability based on estimated risk of an adverse outcome such as injury or death of the targeted subject due to electrical stimulation, or alternatively failure of the weapon to deliver sufficient stimulation to incapacitate the subject, rather than acceptability based on simple conformance to specified limits of performance.
To summarize the limitations described above, the prior art does not provide apparatus or method which will permit an individual who is not skilled in the art of high-voltage engineering and related laboratory technique, such as a peace officer, to measure and analyze the electrical output of a conducted energy weapon and in so doing derive an estimate of the risk of electrically stimulating a targeted subject to the point of serious injury or death.
Furthermore, the prior art does not provide apparatus or method which would permit a non-technical individual, such as a peace officer, to measure and analyze the electrical output of a conducted energy weapon and in so doing derive an estimate of the risk of failing to sufficiently stimulate a targeted subject to achieve incapacitation. The prior art does not provide machine-based automation which would permit a non-technical individual, such as a peace officer, to make such technical and analytical determinations rapidly and easily, and in a way which is non-hazardous for the officer concerned.
To address concerns of the general public in regard to CEW safety, an object of the present invention is to provide apparatus for testing a CEW, the apparatus including analyzer means to produce characteristic signals representative of characteristics of electrical current pulses delivered by the weapon into a resistive load when the weapon is discharged, where such characteristics include peak values, durations, and instantaneous frequencies of the pulses, and integrated areas of the pulses which thereby represent net electric charge. Risk estimation means compares each characteristic signal to corresponding thresholds representing increasing severity of harm due to electrical stimulation. By counting the number of times a characteristic signal exceeds a corresponding threshold, the risk estimation means thereby produces an estimate of the risk of injury to a targeted subject due to electrical stimulation. Indicator means displays the risk of injury and warns the user when the risk exceeds a predetermined threshold.
To address concerns of law enforcement in regard to CEW efficacy as a weapon, a further object of the present invention is to provide apparatus for testing a CEW, the apparatus including analyzer means to produce characteristic signals representative of characteristics of electrical current pulses delivered by the weapon into a resistive load. Risk estimation means compares each characteristic signal to corresponding thresholds representing decreasing levels of incapacitation of a targeted subject. By counting the number of times a characteristic signal falls below a corresponding threshold, the risk estimation means thereby produces an estimate of the risk of CEW failure to incapacitate the subject. Indicator means displays the risk of CEW failure to incapacitate and warns the user when the risk exceeds a predetermined threshold.
Advantageously, automated machine-based testing and risk analysis provided by the invention allows weapon tests to be easily and routinely conducted by non-technical persons having no knowledge of electrical principles, laboratory testing methods or risk analysis methodologies, such persons including peace officers or other individuals who may be associated with a law enforcement agency.